AP* Chemistry ATOMS, MOLECULES & IONS
2.1 THE EARLY HISTORY OF CHEMISTRY • • • • The highest honor given by the American Chemical Society. He discovered oxygen. Ben Franklin got him interested in electricity and he observed graphite conducts an electric current. Politics forced him out of England and he died in the US in 1804. The back side, pictured below was given to Linus Pauling in 1984. Pauling was the only person to win Nobel Prizes in TWO Different fields: Chemistry and Peace.
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1,000 B.C.—processing of ores to produce metals for weapons and ornaments; use of embalming fluids 400 B.C.—Greeks—proposed all matter was make up of 4 “elements” : fire, earth, water and air Democritus—first to use the term atomos to describe the ultimate, smallest particles of matter Next 2,000 years—alchemy—a pseudoscience where people thought they could turn metals into gold. Some good chemistry came from their efforts—lots of mistakes were made! 16th century—Georg Bauer, German , refined the process of extracting metals from ores & Paracelsus, Swiss, used minerals for medicinal applications Robert Boyle, English—first “chemist” to perform quantitative experiments of pressure versus volume. Developed a working definition for “elements”. 17th & 18th Centuries—Georg Stahl, German—suggested “phlogiston” flowed OUT of burning material. An object stopped burning in a closed container since the air was “saturated with phlogiston” Joseph Priestley, English—discovered oxygen which was originally called “dephlogisticated air”
2.2 FUNDAMENTAL CHEMICAL LAWS
late 18th Century—Combustion studied extensively CO2, N2, H2 and O2 discovered list of elements continued to grow Antione Lavoisier, French—explained the true nature of combustion—published the first modern chemistry textbook AND stated the Law of Conservation of Mass. The French Revolution broke out the same year his text was published. He once collected taxes for the government and was executed with a guillotine as an enemy of the people in 1794. He was the first to insist on quantitative experimentation. • • • •
THE LAW OF CONSERVATION OF MASS: Mass is neither created nor destroyed.Joseph Proust, French—stated the Law of Definite Proportions
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THE LAW OF DEFINITE PROPORTIONS: A given compound always contains exactly the same proportions of elements by mass. •
1808--John Dalton stated the Law of Definite proportions. He then went on to develop the Atomic Theory of Matter.
THE LAW OF MULTIPLE PROPORTIONS: When two elements combine to form a series of compounds, the ratios of the masses of the second element that combine with 1 gram of the first element can always be reduced to small whole numbers. Dalton considered compounds of carbon and oxygen and found: Mass of Oxygen that combines with 1 gram of C Compound I 1.33 g Compound II 2.66 g Therefore Compound I may be CO while Compound II may be CO2. Exercise 2.1 Illustrating the Law of Multiple Proportions The following data were collected for several compounds of nitrogen and oxygen:
Mass of Nitrogen That Combines With 1 g of Oxygen Compound A Compound B Compound C
1.750 g 0.8750 g 0.4375 g
Show how these data illustrate the law of multiple proportions. A = 1.750 = 2 B 0.875 1 B = 0.875 = 2 C 0.4375 1 A = 1.750 = 4 C 0.4375 1
Atoms, Molecules and Ions
2.3 DALTON’S ATOMIC THEORY Dalton’s ATOMIC THEORY OF MATTER: (based on knowledge at that time): 1. All matter is made of atoms. These indivisible and indestructible objects are the ultimate chemical particles. 2. All the atoms of a given element are identical, in both weight and chemical properties. However, atoms of different elements have different weights and different chemical properties. 3. Compounds are